Displaced-Axis Dual Reflector Antenna

It's difficult to offer advice without having a clear picture of what you are trying to do and what the tolerances ought to be.

I know there is a suggested standard for 80% illumination of a reflector. if you know the beam-width of your horn, the rest should be an easy guess.

Usbport, davismatteson thank you for your replies.

ADE is a kind of reflector antennas which are designed in assumptions of validity of Geometric Optics (GO) laws, especially - all linear distances are much larger than wavelength is.

My attempts to design an antenna ADE by means of ratios available for instance in Modern Antenna Design, 2nd Edition by Thomas A. Milligan (2005), p. 421-424, have resulted in a 42 mm distance (Ls) between a feeder aperture (and its phase center) and a subreflector.

In most cases the far zone distance (R₀) for any antenna may be calculated as R₀=2*d²/λ. This value is proposed to be a minimum distance at which antenna (particularly, feeder) directional properties are formed and emission radiated may be assumed to be a spherical wave, near antenna fields are absent or negligible.

For the aperture diameter of the feeder - 90 mm, wavelength ~ 79 mm R₀ ≈ 205 mm.

It is obvious that the laws of GO are not quite fulfilled in this case. The feeder can not be assumed to be a point source. That is why the amplitude-phase distribution of the aperture field in the antenna can be not desired, directional properties and antenna gain will not be optimum.

Prompt me information sources which can help in an evaluating of antenna efficiency vs. the distance between the feed and the subreflector along the antenna axis in ADE please.